Question

) Explain the difference between a direct and indirect observation. Provide an example of each not found in the “Error in Surveying” reading. What is the definition of an error? Why can we not calculate an exact error?

Answer 1

Ans.) Direct Observation - Direct observation is a method of collecting evaluative information in which the evaluator watches the subject in his or her usual environment without altering an environment. In this, investigator does not create an artificial situation. An observation form keeps observations consistent. For example- measurement of a single angle.

Indirect Observation - Indirect observation involves studies of mechanical recording or the recording by some of the other means like photographic or recording. In this, observed value is deduced from measurement of some related quantities. For example - measurement of a summation angle for the sum of an angle by repetition.

Definition of error :-

Error - The error in a surveying measurement is defined as the difference between the measured value of a parameter and its true value. Types of errors are instrumental, personal and natural errors.

Therefore, Error = Measured value - True value

Let, e = error

x₁ = measured value

x₂ = true value

so, e = x_{1 -} x₂

Difficulty in measurement of exact error :-

Errors may also be due to various natural factors such as temperature, humidity, wind, refraction, and magnetic declination which makes an investigator difficult to calculate the exact error. Therefore, we cannot claculate an exact error.